Crankcase lubricating oils must provide minimal frictional wear in an engine over a wide range of operating temperatures. These engine temperatures can range from below freezing during cold weather starting to above 400.degree. F. (200.degree. C.) during severe usage. Lubricants which meet SAE viscosity specifications for both low and high temperatures are known as multigrade oils.
Blending basestocks of different viscosities is one way of formulating a multigrade oil. Merely blending basestocks of different viscosities, however, may not enable the formualtors to meet the low and high temperature viscosity requirements of some multigrade oils let alone other properties such as volatility and seal compatibility. The formulator's primary tool for meeting multigrade oil viscosity requirements is an additive referred to as a viscosity modifier.
An alternative means of reducing the basestock viscosity is to employ so-called non-conventional lubricants (or NCL). Examples of NCLs are synthetic basestocks such as polyalphaolefin oligomers (PAO) and diesters and specially processed mineral basestocks such as basestocks that have been hydro-cracked or hydroisomerised to give greater paraffinic content and lower aromatic content. These NCLs, especially the diesters, are very expensive, may not respond well to conventional antioxidant systems, and may not be fully compatible with standard sealant materials.
Accordingly, it is an object of the present invention to provide an 0W-40 motor oil that has desirable low and high temperature properties.
It is another object to provide a motor oil that is a blend of conventional and non-conventional lubricants.
These and other objects will become apparent upon reading the description which follows.